Have you considered Inon Strobes? Small in size, but big in power and flexibility! They have actually become very popular lately. I just finished setting up a system with a small digital camera and dual Z-240's, and I specifically used the Z-240's. The strobes are probably more than I need at the moment, but my local specialty underwater photography store told me the strobes would be perfect for when I ultimately upgrade to a SLR in a housing.
INON America - Product Catalog Inon Z-240 Strobe [ino.z240] - $749.00 : Reef Photo & Video!, The Underwater Photo Pros